Continuity mistake: When Angel is talking to Cordelia in the garden at the very end of the episode "Supersymmetry" he has a cut on his cheek. The beginning of "Spin The Bottle" is the continuation of that scene, but Angel's face no longer has a cut.
Continuity mistake: After Cordelia kisses Connor, her hand is on his cheek. Just before she says "and if this is the end", in the shot of Connor she removes her hand, then the angle changes to show her, and her hand's suddenly back on his cheek again.
Continuity mistake: When Angel grabs Cordelia's hand as she apologies after telling him to "get over it", the position of Angel's hand changes between shots.
Continuity mistake: When Cordelia looks at the monitor, the reflection of Angelus's cage shows Angelus standing at the bars next to Connor. It cuts to a direct shot, and Angelus is sitting on the ground on the other side of the cage. (00:21:40)
Continuity mistake: When Wesley tells Faith that Angelus is back, she says, "Step away from the glass" and hangs up the phone. When Wesley jumps from his chair (to allow Faith to smash through the glass and escape) you can see Faith behind the glass with her hands up to her face and standing, but in the close up of Faith her hands are at her sides and she is only just getting out of her chair. (00:23:20)
Continuity mistake: When Cordy throws the knife at the door after Willow leaves, the knife hits at an impossible angle from where it was supposed to have been thrown.
Inside Out - S4-E17
Continuity mistake: The sketch of Cordelia that Angel looks at depicts her facing to her left. But once he places it back on Wesley's desk, it depicts her facing to her right, revealing a flipped shot.
Continuity mistake: When Fred is running from the oncoming white car, she runs toward a blue car getting fixed on the side of the road, but jumps out of the way as the white car hits the blue car. Fred hits the ground and rolls over to the fence, but in a following shot it shows Fred only just hitting the ground and she is on the grass, not next to the fence. (00:14:20)
Continuity mistake: When Angel and the others infect Connor with Cordy's blood, Gunn rips open Connor's shirt. In the following shots, the shirt closes and then opens again. (00:41:40)
Continuity mistake: When Jasmine picks up the car and throws it at Angel, it cuts to a shot of Angel moving out of the way then shows the car falling from the bridge. First mistake, Jasmine disappears from the shot when the car is falling, and second, the car falls directly straight and at a higher point than Jasmine actually threw it. (00:35:50)
Answer: Everybody including Angel saw her. After helping them and then being left alone to talk to Angel, Cordelia says that the Powers That Be let her come back one more time to help them. After Angel gets a call saying that she died, he realises that it was her spirit that was helping them the entire time.